1. Field of the Invention
Processes for improving the flow rate of an aqueous system comprising adding natural polymer to the aqueous system, and then adding a synthetic polymer to the aqueous system. The natural polymer may be a polysaccharide, such as dextran.
2. The Related Art
In the production of valuable metals and minerals in mining, ore bodies are typically ground, dispersed in aqueous solutions, treated with agents, and subjected to various processing conditions (temperature, pH, pressure, shear rate). The intended result of the mining operation is to generate aqueous dispersions that will undergo isolation, separation, or purification of the valuable portion of the ore, whether it is a metal or mineral.
Aqueous dispersions that result from the subject mining operations are comprised of mixtures of water, solids, and other materials. Examples of the types of solids typically found in the aqueous dispersions from mineral operations include minerals, metals, metal oxides, metal sulfides, metal hydroxides, salts, organic matter, and other inorganic matter. Aqueous dispersions that are comprised of ores, concentrates, tailings and the like, which may contain particles that have morphologies that are not conducive for rapid sedimentation or pumping are of particular interest. The pumped concentrated aqueous dispersions may contain valuable minerals or metals or waste residues. Valuable resources found in the aqueous dispersions may include minerals (bauxites, latherites, or sulfides), metals (such as iron, base metals, precious metals, light metals, and uranium), coal and the like. The waste streams consist of gangue minerals and other constituents with little or no value. Typically, aqueous dispersions are processed by treatment with flocculating or coagulating agents to initiate liquid-solid separation that concentrates the solids portion of the aqueous dispersion in appropriate separation processes, e.g. centrifuging, concentrating, sedimentation, dewatering, filtering and the like.
Liquid-solid separations facilitated by the use of coagulating and/or flocculating agents are required to further concentrate the aqueous dispersions to reduce the process costs associated with transport, calcination, separation, digestion, or storage. Liquid-solid separations are now more challenging because ore bodies that are processed today contain lower concentrations of the valuable minerals and metals and higher concentration of gangue minerals. Gangue comprises that portion of ore bodies that is unusable or of low value, and gangue typically consists of fine particles of irregular shape. Liquid-solid separations are accelerated by the use of synthetic or natural polymers prior to transporting the aqueous dispersion from where it is found or generated to the facility where it is stored, calcined, separated, or transported. Due to the size and shape of the gangue particles, gangue minerals are more difficult to agglomerate; therefore, higher dosages of synthetic or natural polymer flocculants are required to achieve the same sedimentation rates necessary to maintain desired mill flow rates. What makes the transport of the concentrated aqueous dispersions even more challenging is that the chemicals used to coagulate or flocculate the solids of the aqueous dispersions promote higher rheological parameters, such as higher viscosity or higher yield stress for the concentrated solids and make the solids even more difficult to pump.
Use of high molecular weight, synthetic polymer flocculants imparts higher rheological characteristics making pumping of the aqueous dispersions more difficult, as a consequence operating cost and profitability are negatively impacted. Preferably, concentrated aqueous dispersions should exhibit low yield stresses to allow pumping at low threshold energy levels. Additionally, concentrated aqueous dispersions should possess low viscosities, which should result in fast flow rates through mining processes for improved efficiency, productivity, and lower energy costs at the mills or refineries. In order for mining companies to remain profitable, there is a need for mining operations to be able to process concentrated aqueous dispersions efficiently by reducing the rheological properties of the substrates.